Method of restricting oxidation of sponge iron

ABSTRACT

A SYSTEM FOR REDUCING THE OXIDATION OF AGGLORMERATED SPONGE IRON DURING STORAGE OR TRANSIT WHEREIN THE MASS OF IRON IS STORED IN AN ENCLOSURE HAVING A GAS-PERMEABLE BOTTOM AND AIR, NITROGEN-ENRICHED AIR OR NITROGEN TREATED TO REMOVE MOISTURE AND ACIDIC CONSTITUENTS, IS PASSED THROUGH THE MASS AT A PREDETERMINED RATE.   D R A W I N G

METHOD OF RESTRICTING OXIDATION OF SPONGE IRON Filed May 22, 1970 Nov.28, 1972 H. NAGEL ETAL 2 Sheets-Sheet 1 Y L W E m m H amu wwm m m mtm emmm mw $3M n m METHOD OF RESTRICTING OXIDATION OF SPONGE IRON Filed May22, 1970 Nov. 28, 1972 H. NAGEL E AL 2 Sheets-Sheet 2 N GI 28.: g g Q sQ s a s q 5 ME? 7 Horst NAGE L Wilhelm THUWi Horst: GARBE William HenryBAILEY Egon GOEDEKE Rolf DADAZYNSKI INVENTORS.

United States Patent O 3,704,088 METHOD OF RESTRICTING OXIDATION OFSPONGE IRON Horst Nagel, Bergen Enkheim, and Wilhelm Thumm and HorstGarbe, Frankfurt, Germany, William H. Dailey, Cleveland, Ohio, and EgonGoedeke, Frankfurt, and Rolf Dadazynski, Rod an der Weil, Germany,assignors to Metallgesellschaft Aktiengesellschaft, Frankfurt, Germany,and The Steel Company of Canada Limited, Hamilton, Ontario, Canada FiledMay 22, 1970, Ser. No. 39,630 Claims priority, application Germany, May29, 1969, P 19 27 300.8 Int. Cl. C23f 15/00 US. Cl. 21--2.5 4 ClaimsABSTRACT OF THE DISCLOSURE A system for reducing the oxidation ofagglomerated sponge iron during storage or transit wherein the mass ofiron is stored in an enclosure having a gas-permeable bottom and air,nitrogen-enriched air or nitrogen, treated to remove moisture and acidicconstituents, is passed through the mass at a predetermined rate.

FIELD OF THE INVENTION The present invention relates, in general, to asystem for reducing the oxidation of iron and more particularly to asystem for reducing the oxidation of agglomerated sponge iron duringstorage or transportation.

BACKGROUND OF THE INVENTION It is known that sponge iron, when piled ina mass, such as it is during storage or transit, can oxidize,particularly in the presence of moisture, causing a rise in temperatureof the mass to 80-100 C. or even to the point of ignition, endangeringthe storage or transit means, e.g. a ships hull.

Heretofore, it has been the practice to prevent oxidation of sponge ironby coating it with anti-corrosive agents, such as oil, paraflin orplastics.

However, these methods do not afford adequate protection, are expensiveand leave impurities on the iron.

OBJECTS OF THE INVENTION It is, therefore, an object of the invention toprovide a system for reducing or restricting the oxidation ofagglomerated sponge iron during storage or transit.

Another object of the invention is to provide a method of limitingoxidation of sponge iron in lump or agglomerated form which isrelatively inexpensive and free from the indicated disadvantages.

Still another object of the invention is to provide a system for thepurpose described that does not deposit impurities on the iron.

SUMMARY OF THE INVENTION The above mentioned objects, and others whichwill become apparent hereinafter, are achieved by piling theagglomerated or lump sponge iron mass in an enclosure having a series ofgas nozzles formed in the bottom. A gas, such as air, nitrogen, enrichedair or nitrogen, is driven through the nozzles and passes through thesponge iron mass, which is gas-permeable or porous.

The rate at which the gas is passed through the mass determines the risein temperature of the mass, so that a rate can be selected to givevirtually no rise in temperature or a rise only to the highestpermissible limit.

It has been found that the rate at which the gas should be passedthrough the mass is about 5-160 cubic meters per square meter-hour,depending on the height of the mass.

Although it has been found that the oxidation rate and resultanttemperature rise are primarily dependent on the rate of gas flow, themoisture content of the gas is a major contributing factor in theoxidation of the iron mass. To this end, a dehumidifier is provided toremove moisture constituents present in the gas, prior to passagethrough the mass. The dehumidifier may drop the temperature of the gasto about 20 C., a heater is provided to bring the gas to about 30 C.,the gas being then driven into the enclosure by a blower, at awater-vapor partial pressure as low as possible.

Under certain circumstances, it is advantageous to collect and recyclethe gas, in which case, in addition to the dehumidifier, heater andblower used to treat the gas, a lime filter is used to remove any acidconstituents which may have been picked by the gas passing through theiron mass. When atmospheric air is employed, even without recirculation,acid constituents such as CO S0 and S0 are removed by this filter.

Because such acid constituents have a strong oxidizing action, thismeasure further reduces the oxidation of the mass.

The invention is based upon our surprising discovery that in spite ofthe fact that the oxidation-limiting gas may contain oxygen andeventually bring about more contact of iron surface with oxygen than astatic system in which an ambient atmosphere lies in contact with spongeiron, the circulation of the gas through the mass materially limitsoxidation. We believe that the degree of oxidation is a function oftemperature and, whereas a temperature buildup occurs in the staticcase, the displacement of the gas through the mass according to theinvention prevents such buildup.

It has been found further that any steps which reduce the water vaporpressure in the gas supplied to the enclosed pile bring about a greaterreduction in the tendency toward oxidation. Such reduction of the H 0vapor pressure can be effected by dehumidification using a cooler tobring the temperature of the gas below the dewpoint and condense watertherefrom, absorption to remove water without changing the gastemperaure, or heating to reduce the relative humidity. Since a cooleris used to lower the temperature of the gas below the dewpoint, it isapparent that the gas circulated through the iron mass is at atemperature above the dewpoint (at most 45 C. as seen in curves b and din FIG. 2), and that the water-vapor partial pressure is below that ofthe dewpoint at the gas temperature used.

Best results are, of course, obtained with minimum oxygen content in thegas stream so that nitrogen or nitrogen-enriched air is used preferably.After the initial passage of air through the mass, however, the oxygenconcentration is slightly reduced, thereby enriching it with nitrogen.It is preferred, therefore, to recirculate this gas, abstracting theheat picked up in its passage through the mass.

The rate at which the gas is supplied depends upon DESCRIPTION OF THEDRAWING The above and other objects, features and advantages of theinvention will become more readily apparent from 3 the followingdescription and specific examples, reference being made to theaccompanying drawing, in which:

FIG. 1 is a diagrammatic view of the apparatus according to theinvention; and

FIG. 2 is a graph illustrating results of the process according to theinvention.

SPECIFIC DESCRIPTION The enclosure 2 shown in FIG. 1 has cylindricalwalls 2' and a perforated conical bottom end 2" supporting thesponge-iron mass. A removable lid 3 is provided at the top of enclosure2 for introducing agglomerated sponge iron therein. The sponge ironforms a gas-permeable mass 1, which can be removed by means of a door 4provided at the apex of the conical bottom 2".

A series of gas nozzles 5 are provided in an array along the insidewalls of the conical bottom 2". The nozzles 5, which introduce a gassuch as air, nitrogen-enriched air or nitrogen, into the enclosure 2,are supplied by conduits 5' equipped with regulating valves 5".

The conduits 5' are supplied with warm gas at 30 C. from a heater 6 viaa single conduit 6, the heater 6 being supplied by a blower 7.

The blower 7 and heater 6 form part of a recycling system which startswith the introduction of the aforementioned gas into the enclosure 2 viathe nozzles 5. The gas is passed through the mass 1 at a rate of 5 to160 cubic meters per square meter-hour, depending on the height of thepiled mass 1. By way of example, if the height of the piled mass is 1 to3 meters, the required rate is 5 to 40 cubic meters per squaremeter-hour, preferably 8 to 25 cubic meters per square meter-hour. Ifthe mass height is 3 to 8 meters, the requirement is 10 to 80 orpreferably to 50 cubic meters per square meterhour. If the height of themass exceeds 8 meters, the requirement is 20 to 160 or preferably 40 to100 cubic meters per square meter-hour.

After the gas passes through the mass 1, it is drawn off at outlet 8into a dehumidifier 9, where the cooling coil 9 condenses the moisturethat the gas picked up passing through mass 1, the liquid condensatebeing drained through an outlet valve 9" provided at the bottom ofdehumidifier 9.

After passing through the dehumidifier 9, the gas, which has been cooledto 20 C., is drawn through conduit 10' into a lime filter 10, where theacid constituents picked up from the mass 1 are removed.

Upon leaving the filter 10, the gas is drawn into the blower 7,completing the cycle.

In FIG. 2, a graph representing some test results is shown.

The time in hours is plotted along the abscissa and the temperature, inthe upper region of the iron mass, in degrees centigrade along theordinate. Percentages recited relate to water content of the gas.

The curve a shows the rise in temperature of the mass when 5% water ispresent in the still atmosphere and no gas is passed through.

Curve b shows the temperature rise of the mass when 5% water is presentand air is passed through at a rate of cubic meters per squaremeter-hour.

Curve 0 shows the temperature rise of the mass with a 0.19% watercontent and no air circulation.

The results shown in FIG. 2 were obtained with a vessel of 0.5 meterdiameter and 3 meters height using 830 kg. of sponge iron (fresh) foreach set of tests.

We claim:

1. A method of preventing oxidation of sponge iron, comprising the stepsof piling and enclosing agglomerated sponge iron to form a gas-permeablemass; passing a gas selected from the group consisting of air andnitrogenenriched air through said mass at a rate of 5 to 160 standardcubic meters per square meter-hour, and suflicient to prevent thetemperature in said mass from rising above substantially 45C.; anddehumidifying said gas prior to passing it through said mass to maintainthe water vapor partial pressure below that of the dewpoint at contactwith said mass.

2. A method of preventing oxidation of sponge iron as defined in claim1, wherein the gas is dehumidified by cooling followed by the step ofwarming said gas prior to passing it through said mass.

3. A method of preventing oxidation of sponge iron as defined in claim1, further comprising the steps of:

collecting said gas after passing it through said mass;

recycling said collected gas through said mass, said gas picking up acidconstituents upon traversal of said mass; and

deacidifying said gas prior to passing it through said mass.

4. A method of preventing oxidation of sponge iron as defined in claim 1wherein said gas is passed through said mass at a rate with respect tothe height of the mass in accordance with the following table:

Height: Gas-flow rate 1 to 3 meters 5 to 40 m. /m. -hr. (STP) 3 to 8meters 10 to m. /m. -hr. (STP) 8 meters 20 to m. /m. -hr. (STP)References Cited UNITED STATES PATENTS 2,156,357 5/1939 Simson 2l2.5 UX2,160,831 6/1939 Colby et a1. 212.5 UX 2,616,780 11/1952 Atkinson et a1.212.5 3,111,371 11/1963 Bull 212.5 3,188,166 6/1965 Dietz et al. 212.53,551,215 12/1970 Claiborne et a1. 75-26 UX 3,562,780 2/1971 Risenberg75-26 FOREIGN PATENTS 649,735 1/1951 Great Britain 21--2.5

BARRY S. RICHMAN, Primary Examiner US. Cl. X.R. 750.5 R

